Process for sweetening hydrocarbon oils



Patented July 16, 1940 UNITED STATES PATENT OFFICE raooass FOR swaa'rnnmc. HYDRO- oaanou oms No Drawing. Application November 17, 1939, Serial N0. 305,036

12 Claims.

Our invention relates to the sweetening of hydrocarbon oils and more particularly has reference to improvements in the conventional doctor treatment for the removal of mercaptans from light hydrocarbon distillates such as gasoline, naphtha, kerosene, benzine and petroleum oils in general.

It is a principal object of the invention to render the doctor treatment more rapid and economical and to produce sweetened distillates of unusually desirable properties.

' The doctor treatment has long been applied to petroleum oils for the removal of mercaptans.

m It involves treatment of the oils with elementary sulfur and an aqueous alkaline solution of sodium plumbite, known as the doctor solution. The plumbite solution effects a chemical reaction between the mercaptans and the elementary sulfur, resulting in the conversion of the mercaptans to dialkyl disulfides and also into some trisulfide, while the sulfur is converted mainly into sulfides, polysulfides, thiosulfates, etc.

In practicing the conventional doctor treatment, an excess of elementary sulfur is used to bring about a break," a term used in the art to indicate the settling or subsidence point in the doctor treatment. That is to say, the amount of free sulfur used is in excess of the theoretical quantity required to convert the mercaptans into 30 disulfide's and other innocuous compounds. the

excess serving to induce the break in the treatment. Such use of elementary sulfur'to effect settling or subsidence results in the incorporation "of sulfur into the distillate, with its attendant objections. Among these objections, in the case of gasoline, are poor inhibitor and tetraethyl lead susceptibility, lowered antiknock value, increased corrosive action on metals, poor color-and odor stability, and in- 40 creased tendency to form gum.

Although doctor treatment in its many variations is well understood in the art, it may be well to emphasize, by a suitable reference, the circumstances and conditions attending a break 45 and the difficulty of coagulating the colloidal black precipitate.

Doctor plants differ in the way in which doctor solution and sulfur are mixed with the gasoline and the length of time they remain in contact. It is common practice to add the sulfur in gasoline solution before, at the same time as, or after the gasoline and doctor solutions are mixed. The mixing may be done by orifice plates, 55 bamed pipes, pipes withright-angle bends, or

mechanical mixing devices, and mixing time ma vary from a few seconds to several minutes.

When sulfur is added to a mixture of gasoline and doctor solution, the'oil becomes orange-red 'in color; after a longer or shorter time, depend- 5 ing on the gasoline and the amount of sulfur added, the break takes place, when the color disappears and a red-brown to black precipitate, usually called lead sulfide, forms and settles.

In different plants, the break may be pro-- duced as the gasoline leaves the mixers or it may not occur until after the gasoline has entered the settling drum. If a plant has adequate mixing (the proper time of mixing will depend on the type of gasoline and somewhat on the degree of sourness), the gasoline may be allowed to break as it leaves the mixers, and the amount of sulfur required to do this will not be so great as to harm inhibitor susceptibility. However, if a plant has little mixing equipment (a common ,20 installation is three mixing nozzles in about six feet of, line, which for most gasoline is much less mixing than is desirable), a break cannot be obtained in the mixers without using a considerable excess of sulfur, with consequent detri- Z5 ment to the inhibitor effectiveness. If, however, the break in such plants occurs in the firstsettler from three to fifteen minutesv after the gasoline leaves .the mixers, the results from an inhibitor standpoint will usually be satisfactory.

But when the break occurs in the settler, the gasoline being no longer in contact with doctor solution, ittends to produce a finer precipitate, settling more slowly than when the gasoline is broken out while still in contact with doctor solution. As plants deficient in mixing equipment arealso often lacking in settling capacity, the treater in such cases faces a serious dilemma. If he'uses excess sulfur, his gasoline settles well but inhibitor susceptibility is poor; if sulfur is.40 kept down, the gasoline breaks and settles slowly and lead sulfide leaves the plant suspended in the gasoline. (Industrial 8: Engineering Chemistry, vol. 30, No. 11, Nov. 1938, p. 1276).

Thus, in actual practice, the present trend has been to continue to use sulfur as a break inducer, insofar that no universal and economic solution of the problem has been heretofore available. Some effort has been made to solve the problem by subsequent washing with aqueous solution, but this has resulted in attendant loss of expensive lead. Another approach to the problem concerned the use of sodium oleate, sodium resinate, sodium stearate, sodium palmitate, and othersimple unmodified fatty materials 56 as break inducers for replacing a part of the sulfur which is ordinarily used as a break inducer. It is not believed that such procedure is ordinarily applicable as a complete substitute for sulfur as a break inducer. Or, in other words, it is not believed that any attempt has been made to apply such process in instances where the amount of elementary sulfur represented only theoretical quantities and which would necessitate that the oils by means of plumbite solution and elemenethylene glycol .to yield ethylene glycol monoetc.

lead to esteriflcation of all of 'droxylsof the polyhydric alcohol.

tary sulfur, to effect the settling or subsidence in the known sweetening process.- More specifically, the materials contemplated for use as break inducers in the present process are esters ob-- tained by partial esterification of polyhydric alcohols with ricinoleic acid.

As herein used, the term polyhydrio alcohol refers to aliphatic alcohols containing two or more hydroxyl groups and is intended to include such compounds as glycerol, ethylene glycol, beta-methyl glycerol, 1,3 propanediol, pentamethylene glycol, alpha, beta, gamma pentanetriol, sorbitol, mannitol, and the like, and also the polyhydroxy ether alcohols such as diglycerol, triglycerol, diethylene glycol, etc. Such polyhydrlc ether alcohols may also be produced by ether formation from two or more different polyhydric alcohols to yield compounds such as ethylene glycol monoglyceryl ether, 1, piopa- 'nediol 'monoethylene glycol ether, diethylene glycol mono'glyceryl ether, etc. Suitable polyhydroxy ether alcohols .may also be produced from a polyhydric alcohol containing three or 7 more hydroxyls and a monohydric alcohol. Ex

amples of such compounds are glycerol monobutyl ether, glycerol monoallyl ether, pentanetriol I monoethyl ether, diglycerol monopropyl ether,

Thefesters contemplated for use-as break inducers in the present process maybe prepared by direct esterlfication of the polyhydric alcohol with ricinoleic acid in the presence of'a catalyst such as dry hydrochloric acid gas. With such a procedure, the proportions of reactants and conditions of reaction must be adjusted so as not to the available hy-- The break inducers'of the present process may also be produced by other methods which are'well known. For example, trigicinolei'n may be reesterified with glycerol to yield monoricinolein,- or hutyl' ricinoleate may be re-esterlfled with ricinoleate. A large number of different, reesterlflcation reactions of this type arepossible.

'Instead of employing a polyhydric alcohol'for the preparation of the break inducer, one may start with a chlorhydrin. For example; monorincinolein may be obtained by the reaction of. yceryl monochlorhydrin:

cmcicmon) .crmom and ricinoleic acid or a salt of ricinoleic acid, such as the sodium v or potassium salt. qther chlorhydrins may be-prepared in a manner similar to the procedure employed in the manufacture of glyceryl monoclilorhydrin; and from these compounds other suitable esters of ricinoleic acid .maybe prepared.

effected where one where OH.R..COO represents the ricinoleic acir radical, T represents a polyhydric alcohol residue, such as a CsHs, or a CsHm residue, etc., m i: the numeral one or more, and n is the numerai one or more but not necessarily the same as m.

The break inducers represented by the above formula may be used as such, or, if desired, some of the residual hydroxyls may be esterified with aliphatic monocarboxy acids containing less than eight carbon atoms. The finished product, however, must contain atleast one free hydroxyl group attached to the polyhydric alcohol residue. For example, tetraglyceryl monoricinoleate contains 5 residual hydroxyl groups attached to the tetraglyceryl radical. Four of these hydroxyls might be esterified with aceticacid to yield a suitable break inducer.

Such partial esterification of residual hydroxyl groups with lower fatty acids containing less than I 8 carbon atoms leads in some cases to improved solubility of the compound in petroleum distillates. In the claims, the above formula is used and is intended to include those compounds obtained on partial esteriflcation of residual hydroxyl groups with lowerfatty acids containing less than 8 carbon atoms.

Our preferred break. inducers are glyceryl monoricinoleate and glyceryl diricinoleate.

The compounds herein disclosed are preferably used as the sole break inducer for the doctor treatment, in which event the quantity of 'ele mentary sulfur employed in the doctor treatment is not in excess of the theoretical amount required to convert the mercaptans. In this preferred operation, where no appreciable excess of sulfur is used in the doctor-treatment, there is effected a faster break than can be obtained by means of other break inducers and frequently a. break is effected where one might not be otherwise obtainable. Additionally,there is recovered a distillate which is free of excess sulfur, an im-' portant advantage as has already been indicated.

However, the invention is not limited to the use. of the organic compounds referred to as the sole break inducer but they may be employed in be used in the doctor treatment, the excess func- "tioning with the compounds of this invention to bring about the desired break in the treatment. The advantages of such operation are that relatively little sulfur is required, the break is in duced very rapidly, and frequently a breakis cannot be obtained at all by means ofsulfur alone. I

As to the preferred operation-above indicated,- it willbe observed that the doctor treatment differs from that heretofore employed'in that quantity of elementary sulfur added isonly the theoretical amount based on stoichiometrical calculations, or other comparable test, to convert mercaptans to disulfides and otherinnocuous compounds, there being present during the treatment no excess of sulfur capable of com- 7 pletely or partially acting as a break inducer. Elementary sulfur, if present in suflicient excess in the sweetened distillate, can be detected by the doctor test with the addition of a mercaptan such as ethyl or butyl mercaptans For instance, a sweetened gasoline containing an excess of elementary sulfur no longer shows positive in the doctor test. However, if there is a slight excess of elementary sulfur present, this elementary sulfur can be detected by the addition of butyl mercaptan or the like, followed by a doctor test on the admixture. A large excess may be indicated by the less sensitive copper strip test.

The butyl mercaptan test, referred to above, is commonly used in a qualitative manner to detect excess elementary sulfur. This test is described in the UniversalOii Products Co. Bulletin No. 22, p. 15, as follows:

In doctor sweetening, the most important factor in securing inhibitor effectiveness, is to use the smallest possible amount of sulfur. Sulfur addition may be controlled by testing with mercury or butyl mercaptan. In making the butyl mercaptan test, a sample of gasoline drawn from the doctor plant after it has left the mixers is allowed to stand until the lead sulfide has settled, and 30 cc. filtered into a4 ounce oil sample bottle. 20 cc. of a 1 to 1,400 solution of butyl mercaptan is added and 10 cc. of doctor solution.

The mixture is shaken for 15 seconds and observed. The' sample should be green-yellow. It will slowly become opaque but should remain yellow in color even if observed for 30 minutes.

If it turns orange or brown, excess sulfur has been used, and on addition of inhibitor the gasoline will have lower inductionperiod and higher copper dish gum than would have resulted had less sulfur been used."

The chemistry of the reactions whicn enter into doctor sweetening is rather complex and not completely understood. However, it is common practice, for the purposeof calculating the amount of sulfur necessary, to use the following reaction as being representative:

Wherein It represents the hydrocarbon group of a mercaptan or disulfide.

The amount of sulfur required for completion of these reactions may be calculated from the original mercaptan content of the distillate. With some distillates; the sweetening reaction appears to lead to the formation of stable trisulfides, rather than disulfides. In this case the reactions presumably proceed as follows:

With distillates where these reactions take place, the theoretical sulfur requirement may becalculated by use of the above equations and the known original mercaptan content of the distillate. However, for all practical purposes, the butyl mercaptan test, previously described, may be used as a test for whether or not excess sulfur has been used. Accordingly, the "term negative to the butyl mercaptan test, as applied to sweetened distillates, is used herein to mean that a distillate has been sweetened with the theoretical amount of sulfur, or that the minimum amount of sulfur necessary for completion of the sweetening reaction has been'employed. The

reason for this is.that' the butyl mercaptan test may be made more easily and more quickly than a determination of the actual course or nature of the sweetening reactions.

As is understood, of course, if hydrogen sulfide is present, allowance must be made for the amount of lead required to remove such sulfide. However, this is not apt to be a factor requiring consideration, due to usual preliminary removal of hydrogen sulfide.

In view of what has been said previously, it is obvious that the satisfactory application of the doctor treatment must involve a rapid and complete separation of lead sulfide and associated insoluble material, as soon as the mercaptans are converted into disulfides or other more innocuous compounds. Although the above reactions indicate only precipitation of lead sulfide, it has been found that in reality a precipitate may contain a comparatively small amount of lead sulfide; and there may also be present various complex materials, part of which at least are organic in nature and may represent basic mercaptides. The equations indicate that thesubsidence or settling of the black precipitate,

is not so definite. As a mater of common practice, sulfur is added in the conventional doctor treatment for two distinct purposes of converting mercaptans and inducing the break; and these two purposes must be fully appreciated in order to understand the benefit obtained by applying the improved procedure which constitutes our present invention,v particularly in its preferable form, i. e., where the complex organic compounds herein described are used as the sole break inducer, with only the theoretical amount of sulfur to convert mercaptans or to give a negative butyl mercaptan test.

It has heretofore been proposed to employ water soluble soaps to effect the break in doctor treatment, the soaps being utilized in ratios of 1 to 2500 or 1 to 7500. At such ratios, the common soaps are often ineffective and hence there is the tendency to employ just as much sulfur as if no soap had been added. In contradistinction to the common soaps heretofore contemplated, the break inducers of the present invention are invariably effective and invariably enable a marked reduction in the amount of sulfur needed in the doctor treatment, even to the extent, as in the preferred embodiment already described, of limiting the sulfur to the theoretical amount necessary for converting the mercaptans into innocuous compounds.

The break inducers of this invention need be used in only very minute quantities, for example, in ratios varying from 1 to 5000 or 1 to 7500 or even 1 to 75,000, based on'recovered or sweetened gasoline or other distillate treated. To the extent that our improved break inducers possess the property of forming oil-in-water emulsions, it

should be observed that they are employed in such insignificant quantities that they do not exspecific conditions surrounding the particular operation, for purposes of brevity, we will describe only the preferable form of procedure, 1. e., wherethe herein disclosed organic compounds are used as sole break inducers. It is obvious, however, that those skilled in the art and acquainted with such procedure could readily modify the conventional doctor treatment in which elementary sulfur is used as a break inducer, so

.as to reduce the amount of sulfur employed, and

offset that reduction by suitable break inducers of this invention.

In a continuous doctor sweetening plant, the organic-break inducer is added continuously to the stream of sour distillate prior to its admixquantities of the ture with doctor solution and sulfur. When the break inducer is a liquid; this is conveniently done by means of a small injector pump adjusted to deliver the break inducer in some definite, desired amount, usually within the limits of one part per 7500 to 75,000 parts of gasoline. After the introduction of break inducer has begun, the amount of sulfur added to the distillate, or to themixture of distillate and doctor solution, is decreased tothe theoretical amount.

In batch system doctor sweetening plants, the

required amount of break inducer is introduced into the sour distillate and mixed thoroughly before the treatment with doctor solution and sulfur. In this case, also, the amount of sulfur used is reduced to the theoretical amount.

In both batch and continuous operation, the

- break inducers of this invention should be added tothe sour distillate prior to the admixture of the latter with the doctor solution, in order to avoid saponification thereof and resultant conversion into soaps. The esters herein employed appear to react rather slowly with the doctor solution, so that their action as break inducers is probably complete before any major portion thereof is saponified or otherwise altered by contact with doctor solution.

Inorder to indioate'the effectiveness of the present process, attention is directed to the following table. The gasoline employed in the present instance was'obtained from East Texas crude petroleum. The figures given refer to tests made with 100 gram portions 'of gasoline:

excess of elementary sulfur resulted in a posi-- tive butyl mercaptan test. When an efiort was -made to substitute the common soap type of break inducer for elementary sulfur, it was found that its use, in amount equivalent to times the amount of sulfur required for break induction, did not give satisfactory results. For instance, when the 2 milligram excess of elementary sulfur was replaced by milligrams of sodium stearate, a good break was not obtained; This same condition prevailed when a similar amount of sodium oleate or sodium resinate or castile soap was employed. When there was added only the amount of elementary sulfur required to complete the chemical reaction and it was attempted to depend on the addition of sodium stearate, sodium oleate, castle soap or sodium resinate, as sole break in ucers, a satisfactory break was not obtained ev n when these compounds were to the results above indicated, attention is directed to the results obtained when employing the break inducers herein contemplated for use in the doctor treatment.

It is' to be noted that the break inducersof this invention were used in a ratio of 1 to 20,000

and 1 to 10,000 and in each case, an excellent employed in a ratio of 1to 5000. In comparison break was obtained even though there was no sulfur available for break induction, or to say it in another way, when the amount of sulfur employed was only suflicient to completethe chemical reactions involved. In each instance, since there was no excess sulfur employed, the butyl mercaptan test obviously has to be negative. Since the butyl mercaptan test hadto be negative, it followed that the gasoline was of a type which was free from certain inherently objectionable qualitieswhich are common when Mg. of Actual break in- Butyl mersulfur re- Mg. of Character of Doctor test i iired sulfur ggg figa break on distillate g ggfig (t eory) used treated 3. 0 3. 0 0 None 3.0 4.0 -0 0I 3. 0 5. 0 0 Negative- Positive. 3.0 3. 0 0. 0002 3.0 4.0 0.0002 Positive.

3. 0 3.0 0.0002 3. 0 4. 0 0. 0002 Positive. 3. 0 3. 0 0. (X102 3. 0 4. 0 0.0002 Positive. a. o a. 0 0.0002 3.0 4.0 o I 0.0002 Positive. 3.0 3.0 'Glyoeryl monoricinoleate. 0 00005 Negative. 3. 0 3. 0 Ethylene glycol monoricino- 0. 0001 ea c.

Examination of the abbve table emphasizes the numerous salient points previously discussed. For instance, reference is made to those tests in the above table which are concerned with the use of the common, rather simple, type of break inducer, to wit, materials such as sodium stearate, sodium oleate, castile soap, sodium resinate I and the like.

Furthermore attention is directed to the first three tests which indicate the results obtained when sulfur alone is used as the break inducer. It is to be noted that in the tests as conducted,

of manufacture may result in the production of.

a mixture of a number of break-inducing com- 'butyl mercaptan test and insuflicient to effect pounds rather than a single com und Settling or subsidence; and inducing a break in technically or chemically pure state. Moreover said treatment by adding to the oil a relatively a break inducer of this invention may be emsmall amount a partial esteriflcation product 5 played in admixture with other types of break .of a lyhydric alcohol with ricinoleic acid. inducers for which we-have flied separate appli- 5. Inthe sweetening of sour hydrocarbon. oils cations. by treatment with doctor solution and elemen- Frequently, the compounds or this invention tary sulfur, the method of inducing a break in have beneficial effects in addition to bringing the doctor treatment which comprises adding to 10 about rapid subsidence. For example, as a rethe oil, in a ratio between 1 to 5000 and 1 to sult'oi their use, the amount of black strap 75,000, a partial esteriflcation product of a po yor feathery material appearing at interiaoial surhydric alcohol. with ricinoleic acid.

hydrocarbon oils faces may be greatly diminished or entirely Y In eliminated. I by'treatment with doctorsolution and elemen- 16 It ,is to be understood that the detailed dis- V tary sulfur, the improvement which compri es closures herein are for illustrative. purposes y facilitating the break in said treatment by the and are not to be considered as limitations on addition to the oil of a rioinoleic acid ester 01 the the invention, inasmuch as various modifications general formula (OH.R.COO) m(T) (OH) 1: wherewithin the scope of the appended claims will be n T 1591 pn yhyd c hol re i u and m and .11

are numerals.

to those .I. The improvement as defined in claim 6 tur- 2 apparent Havin g described our invention,- we f y 1 In the sweetening i: o hydrocm-bbn 1 ther characterized in that the element T or said by treatment with doctor solution and elemenester is a glycerol residue. 7 tary sulfur, the meth or inducing a break in The improvement as defined in claim 6 rurgs t o t r i t which comm-is adding t ther characterizedin that the element T or said the sour oil a relatively small amount of a pari a y r l residuetial esterification product of a polyhydrio alcohol 9. The improvement as defined in claim 6 furwith ricinoleic acid. ther characterized in that the element T of said er is a polyglycerol residue containing at least three glyceryl radicals.

10. In the swe 2. A method for sweetening hydrocarbon oils which comprise '30 containing mercaptans sour hydrocarbon oils d elemenetening oi by treatment vwi treating with doctor solution a entrelesulfur, the improvement which comprises mentary suit to conve the mercaptan into facilitating the break in said treatment by the 35 euous o pounds. addition to the oil or glyceryl monoricinoleate. 3 A m t for weetening ar o 11 11. In the sweetening of sour hydrocarbon oils containing mercaptans hich comp adding .by treatment with doctor solution and elemento the oil a part esteriflcation product or a- .tary suliur, the improvement which comp s polyhydric alcohol with ricinoleic and then facilitating the breakdn sa d treatmen by g treating with doctor solution and a quantity or addition to the oil or glyceryldiricinoleate. elemen sulfur not appreciably in exc ss 0 12. In the sweete of sour hydrocarbon oils the theoretical amo t req to conve by treatment-with doctor solution and elemenmercaptans into innocuous compounds. tary suit the improvement which c prises 4. A m thodfior swe h! bun 011 facilitating the break in sa d treatmen bythe 5 containing mercapta which comprise convert addition to'th oil or a cinoleate cont a ing' the mercaptans int innocuous compounds b polyhy o ai hol residue and a hydroiwi group. treatment'o! the oil with alkaline piumbite solution and elementary the amount of ur HARL M. BLAIR; J3.

' t-to render the oil tivcto the 3 IRA S BOYDS'I' 

